A wide variety of compounds for use as lubricating oil or fuel oil additives are known in this art. These include compounds typically referred to as pour point depressants, viscosity index improving compositions, wax crystal modifiers, lube oil flow improvers, and the like. In particular, US-A-2825717 (Cashman et al.) discloses the preparation of certain lubricating oil additives by the copolymerization of polycarboxylic acid esters with other polymerizable monomeric materials, including vinyl compounds such as vinyl acetate. The preferred unsaturated polycarboxylic acid esters therein are fumaric acid esters produced from C.sub.1 through C.sub.18 aliphatic alcohols.
US-A-2618602 (Bartlett) discloses pour point depressing and/or viscosity index improving materials obtained by polymerizing certain specified alkyl fumarate esters. In particular, Bartlett discloses the use of polymerized fumarate esters of C.sub.12 to C.sub.14 alcohols for such purposes. Moreover, Bartlett specifically discloses that the C.sub.12 alcohol was more effective than the C.sub.14 alcohol, although both polymerized esters exhibited pour point depressing properties.
US-A-4088589 (Rossi et al.) discloses the use of specified mixtures of lubricating oil pour point depressants which include polyesters consisting of a polymeric ester of acrylic acid or methacrylic acid and a monohydric alcohol containing from 10 to 18 carbon atoms, and/or interpolymers of a vinyl alcohol ester of a C.sub.2 to C.sub.18 alkanoic acid (e.g., vinyl acetate) and a di(C.sub.6 -C.sub.18 alkyl) fumarate as one of the components thereof for improving the viscosity index of high wax content lubricating oils which also include viscosity index improving ethylene copolymers. Also, US-A-3250715 (Wyman) discloses terpolymers of dialkyl fumarates, vinyl esters, and alkyl vinyl ethers for improving the pour point of lubricating oils, and most particularly in which the dialkyl fumarates are prepared for various C.sub.10 through C.sub.18 alcohols including tetradecyl alcohol alone as well as alcohol mixtures averaging from 12 to 14 carbon atoms.
There has also been disclosed in US-A-4713088 (Tack) the use in various middle distillate fuel compositions for lowering the pour point and controlling the size of wax crystals. These compositions specifically include polymers and copolymers of specific dialkyl fumarate-vinyl acetate copolymers. Most specifically, it discloses the use of such additives in which the average number of carbon atoms in the alkyl groups in the polymer or copolymer must be from 12 to 14. In addition these additives are also disclosed as being useful in combination with the polyoxyalkylene esters, ethers, ester/ethers and mixtures thereof, as well as with various other additives. Furthermore, GB-A-2023645 discloses, for use in treating distillate fuel oils, various three-component systems which include as a first component flow improvers having an ethylene backbone, such as various ethylene polymers including ethylene polymerized with various mono- or di-esters (e.g., vinyl acetate; and C.sub.13 fumarates), as a second component a lube oil pour depressant such as various oil soluble esters and/or higher olefin polymers (e.g., dialkyl fumarate-vinyl acetate copolymers), and as a third component various polar oil-soluble compounds (e.g., phenates, sulfonates, phosphates and carboxylates).
It is also disclosed in US-A-4661121 (Lewtas) and US-A-4661122 (Lewtas) that the size of wax crystals forming in fuels boiling in the range of 120.degree. C. to 500.degree. C. can be controlled by an additive which includes the polymers and copolymers of mono- and di-n-alkyl esters of mono-ethylenically unsaturated C.sub.4 to C.sub.8 mono- or di-carboxylic acids, in which the average number of carbon atoms in the n-alkyl groups is from 14 to 18. These patents show a preference for copolymers of di-n-alkyl fumarates and vinyl acetate, and specifically state that the fumarates can be made from single alcohols or mixtures of alcohols, and when mixtures are used they are mixed prior to esterification. Furthermore, these patents disclose the use of various ethylene unsaturated ester copolymer flow improvers as co-additives therewith, but do not specify that these additives are produced from alcohol mixtures.
Still others have disclosed as a dewaxing aid a copolymer of dialkyl fumarate-vinyl acetate in which a large proportion of the alkyl groups are C.sub.20 to C.sub.24 alkyl groups.
The aforementioned lower molecular weight FVA copolymers are typically formed from a higher temperature exothermic process in combination with the other key operating variables. The conventional process manufactures a FVA copolymer with a weight average molecular weight as measured by a GPC column with a polystyrene standard typically between 20,000 and 50,000 Daltons which can also be correlated to the measurement of specific viscosity which has been measured between 0.2 and 0.3. The conventional preferred way to make this product commercially is to charge the reactor with vinyl acetate and dialkyfulmarate (DAF) in a molar ratio between 0.8 and 0.85. The process is run either in the presence of a solvent such as cyclohexane or run in the absence of solvent. The solvated process maintains the polymerization reaction at about 109.degree. C. The unsolvated process starts at about 94.degree. C., but is allowed to exotherm in excess of 121.degree. C. It is then temperature controlled around a set point of 116.degree. C. The initiator, TBPO can either be added in continuously in the solvated process or added in several discrete additions in the unsolvated process. This is done to moderate the exotherms generated in the absence of solvent. The initiator concentration in the reactor is about 0.15 weight percent of the total.
However, the present inventors have discovered that higher molecular weight (i.e., 50,000 to 350,000 Daltons) FVA copolymers can be made by changes in conventional process conditions, i.e., reaction temperatures, residence time, free radical initiator concentration, number of initiator additions during reaction and the molar ratio of vinyl acetate to dialkyl fumarate (VA:DAF). These higher molecular weight FVA copolymers of the present invention have been demonstrated to significantly improve low temperature properties of formulated oils comprising an alkylene/alkylene viscosity index copolymer.
These higher molecular weight FVA copolymers of the present invention perform particularly well in catalytic and isodewaxed basestocks at competitive treat rates. The performance data presented hereafter demonstrates that higher molecular weight FVA copolymer active ingredient treats in finished crankcase oil can be accomplished if used in an amount of approximately 0.11%, based on the total amount of finished crankcase oil. By comparison, conventional lower molecular weight FVA copolymers require approximately 0.4% active ingredient in the finished oil to pass the stringent low temperature tests. While this benefit is evident in crankcase oils, the present inventors believe that this improvement will allow pour point depressants to be more effective in power transmission fluids, gear oils, tractor hydraulic fluids (THF) and all other industrial lubricants that require low temperature flow and pour point performance. In addition, the higher molecular weight FVA copolymers of the present invention provide a more potent additive for use in fuel treatment, wax and flow improvement applications.